Hot melt adhesives used for disposable products, such as diapers and napkins, are applied to their base materials, for example, nonwoven fabrics, tissues, polyethylene films and the like, and are required to have sufficient adhesion and pressure-sensitive adhesiveness not only at high temperature but also at room temperature.
In recent years, because of an increase in awareness of environmental problems, the replacement of conventional petroleum-derived raw materials by natural materials, plant materials and biodegradable materials has developed. In terms of environmental problems, such as global warming due to an increase of carbon dioxide emission, attempts have been made to produce hot melt adhesives using non-petroleum-based resins, such as polylactic acid-based resins, containing no petroleum as a raw material.
However, in hot melt adhesives containing polylactic acid-based resins, the compatibility between the polylactic acid-based resin and other components, such as a tackifier resin, is insufficient, and therefore, the pressure-sensitive adhesiveness, adhesion, thermal stability and the like tend to be poorer than those of hot melt adhesives using no polylactic acid-based resins.
Japanese Publication No. 2010-155951 discloses a hot melt adhesive comprising a polylactic acid-based resin and poly(butylene succinate) or poly(ethylene succinate). Japanese Publication No. 2004-256642 discloses a hot melt adhesive comprising polylactic acid and a polyvinyl alcohol-based resin. Japanese Publication No. 2002-256250 discloses a biodegradable adhesive comprising polylactic acid and a natural powder substance. These adhesives have insufficient pressure-sensitive adhesiveness at room temperature, and do not have sufficient adhesiveness to base materials of polyolefin and the like. In addition, Japanese Publication No. 5-339557 discloses a hot melt adhesive composition comprising a thermoplastic resin and a tackifier as main components, wherein either one or both of these components comprise a lactic acid copolymer resin derived from polylactic acid or lactic acid and other hydroxycarboxylic acids. For this hot melt adhesive composition, the compatibility between the tackifier and other components is poor, and therefore this hot melt adhesive composition does not have sufficient adhesion to base materials of polyolefin and the like.